Most of the cases, the clear-cell renal cell carcinoma (RCC) express strikingly elevated baseline levels of vascular permeability factor also known as vascular endothelial growth factor (VEGF) rationalized their vascular nature. We originally described the regulation of VEGF A in RCC that is both transcriptional and has mRNA stability and later defined the molecular mechanisms of those pathways. Moreover, it has been shown by our group as well as others that transfection of wild type-VHL (wt-VHL) into RCC cell lines down-regulates VEGF expression that lead to suppression of tumor growth in xenograft models. Despite the positive impact of several anti-angiogenic drugs and multi-kinase inhibitors on progression-free survival and quality of life, disease progression eventually occurs and that leads to rationalize for more studies for better understanding of VEGF biology and its interconnection with tumor biology. Furthermore, several tumors including RCC cells also express high level of neuropilin (NRPs;the non-tryrosine kinase receptor of VEGF) but the downstream signaling events and the subsequent effects on tumor survival, metastasis and progression are poorly understood. Nonetheless, our preliminary data suggest a novel function of VEGF on tumor cells via NRP-1 and that leads to generate a new hypothesis that VEGF/NRP-1 axis can play an important role to maintain the tumor niche or tumorigenic properties of cancer cells. To test our hypothesis, in this competitive renewal application, we have proposed three specific aims. Aim 1 will elucidate the role of VEGF A as a regulator to maintain the dedifferentiated phenotype of RCC cells. Experiments will be performed to examine the importance of VEGF A/NRP-1 axis in tumorigenesis of RCC. Aim 2 will clarify the regulations of downstream effector genes of NRP-1 in RCC tumorigenesis such as: Shh and Notch-1. We will also evaluate the consequences of Np63 null RCC cells on tumorigenesis. Finally, Aim 3 will examine the dependency of renal tumor growth on VEGF/NRP-1 axis in vivo. In this regard, we will extend the tissue culture data and reagents to animal models of renal tumors, seeking to understand the importance of VEGF/NRP1 axis as well as the mechanisms by which it plays an important role in the tumorigenesis. Overall, the proposed experiments will provide new and important information on the mechanisms of carcinogenesis and suggest new targets for intervention in RCC, a common, highly vascular, angiogenesis-dependent carcinoma that is resistant to currently available therapies.